• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.1-8
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• 2005

For study on the unsteady wall interference effect, flows around a circular cylinder in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results showed that the unsteady pressure gradient over the cylinder is enhanced by the wall interference, and as a result the fluctuations of lift and drag are augmented. The drag is further increased because of the lower base pressure. The vortex shedding frequency is also increased by the wall interference. The pressure on the test section wall shows the harmonics having the shedding frequency contained in the wall effect.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.422-429
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• 2001

A two dimensional hierarchical elements are investigated for a use on the incompressible flow computation. The construction of hierarchical elements are explained through the tensor product of 1-D hierarchical functions, and a systematic treatment of essential boundary values has been developed for the degrees of freedom corresponding to higher order terms. The numerical study for the poisson problem showed that the present scheme can increase the convergence and accuracy of finite element solutions, and can be more efficient than the standard first order with many elements. Also, for Stokes and cavity flow cases, solutions from hierarchical elements showed better resolutions and future promises for higher order solutions.

• Journal of computational fluids engineering
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• v.13 no.3
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• pp.1-7
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• 2008

A supersonic base flow is computed to investigate the effect of the eddy viscosity coefficient to the linear ${\kappa}-{\varepsilon}$ turbulence models. Slight modifications to the eddy viscosity coefficient, which are based on the realizability condition, are given to the Launder-Sharma turbulence model so that present models satisfy the realizability condition. Numerical results for supersonic base flow show that turbulence models with the weaky-nonlinear eddy viscosity coefficient can lead to reasonable enhancements in the prediction of the velocity and turbulent kinetic energy profiles.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.382-385
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• 2002

부산 금정산 일대의 평균 수리전도도는 1E-6m/sec ~ 1E--8m/sec차수의 범위로 시험공별로 차이를 보이고 있다. 이 지역에서 지표면의 해발고도(X)에 따른 지하수위(Y)의 상관식 Y =1.00024*X - 3.26725 으로부터 지하수위를 추정하였다. 이 지역에 내린 총 강수량은 함양지역(24,524,131$m^2$)에 연평균강수량(1477.5mm)를 곱한 값(36,234,404㎥/yr)이고, 총 함양량은 기저유출량까지 합한 양(9,073,254㎥/yr)이다 증발산량은 강수량의 약 49%이므로 17,754,858㎥/yr이다. 온천수 사용량은 2,500㎥/day이고, 산성마을의 지하수 사용량은 1,000㎥/day으로 보면, 인위적인 양수량은 1,095,000㎥/yr(강수량의 3%)가 된다. 3차원 지하수유동 모델링 소프트웨어인 GMS package의 MODFLOW를 사용하여 분석한 결과, 금정터널 예정 구간(9.99km)에서의 최대 유출량은 99,200㎥/day이다.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.23 no.2
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• pp.215-226
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• 1993

The purpose of this study was to investigate the effects of the low level irradiation on the mitotic index of the basal cells in the buccal pouch of hamsters{golden hamster: APG strain). After colchicine was administrated to the hamsters through the intraperitoneal, the low level radiation{5460mR) was exposed on the buccal pouch of hamsters. The mitotic index of the basal cells was estimated 2 hours after irradiation. The results were as follows: 1. The mean mitotic index of the control group was 4.32. 2. The mean mitotic index of the irradiated group was 2.46. 3. T-test of data in the irradiated group showed significant difference from the mitotic index in the control group. These results suggested the lowered mitotic index of the irradiated group resulted from the low level irradiation.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.522-528
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• 2011

Artificial basilar membranes made of PVDF(polyvinylidene fluoride) are manufactured using microfabrication processes. The mechanical behavior of PVDF artificial basilar membrane was measured to evaluate its performance as a mechanical frequency analyzer using scanning LDV(laser Doppler vibrometer). The experimental setup consists of the microfabricated artificial basilar membrane, a loud speaker connected to an amplifier for generating acoustic pressure of specific spectral pattern, and a scanning LDV with controlling unit for measuring the displacement of the membrane on the incoming acoustic stimulation. The microfabricated artificial basilar membrane was attached tightly upon a package containing a chamber which can be filled with silicone oil before placed on the experimental setup stage. The experiment results showed that the microfabricated artificial basilar membrane has a property as a mechanical frequency analyzer.

• Journal of the Korea Convergence Society
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• v.10 no.12
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• pp.29-34
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• 2019

If it takes much time to calculate the fitness of the solution in genetic algorithms, it is essential to create a metamodel. Much research has been completed to improve the performance of metamodels. In this study, we tried to get a better performance of metamotel using discrete Walsh transform in discrete domain. We transforms the basis of the solution and creates a metamodel using the transformed solution. We experimented with NK-landscape, a representative function of the pseudo-boolean function, and provided empirical evidence on the performance of the proposed model. When we performed the genetic algorithm using the proposed model, we confirmed that the genetic algorithm found a better solution. In particular, our metamodel showed better performance than that using the radial basis function network that modified the similarity function for the discrete domain.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.9
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• pp.823-831
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• 2011

According to the development of loading equipments, it is usual to change or replace the existing stores. It has been known that pylon-mounted under stores strongly affect aircraft dynamics characteristics due to the change of aerodynamics. To predict the aerodynamics and aero-elasticity is essentially requested with considering the configuration and shape of external stores during the development of aircraft and/or external stores. In this paper, computational fluid dynamics and computational structure dynamics interaction methodology are applied for prediction of aerodynamic characteristics for F-5 aircraft's horizontal tail with various shape of external stores. FLUENT and ABAQUS were used to calculate fluid and structural dynamics. Code-bridge was made base on the globally supported radial basis function to execute interpolation and mapping. As a result, even though the aeroelasticity of the horizontal tail slightly changes according to the shape of external store, the flutter was not occurred at the considered flight conditions in this study.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.3
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• pp.216-223
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• 2005

A computer clock has limits in accuracy and precision affected by its inherent instability, the environment elements, the modification of users, and errors of the system. So the computer clock needs to be synchronized with a standard clock if the computer system requires the precise time processing. The purpose of synchronizing clocks is to provide a global time base throughout a distributed system. Once this time base exists, transactions among members of distributed system can be controlled based on time. This paper discusses the integrated approach to clock synchronization. An embedded system is considered for time synchronization based on the GPS(Global Positioning System) referenced time distribution model. The system uses GPS as standard reference time source and offers UTC(Universal Time Coordinated) through NTP(Network Time Protocol). A clock model is designed and adapted to keep stable time and to provide accurate standard time with precise resolution. Private MIB(Management Information Base) is defined for network management. Implementation results and performance analysis are also presented.

• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.61-72
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• 2011

In order to assess hydrologic and nonpoint source pollutant behaviors in a watershed with Soil and Water Assessment Tool (SWAT) model, the accuracy evaluation of SWAT model should be conducted prior to the application of it to a watershed. When calibrating and validating hydrological components of SWAT model, the Nash-Sutcliffe efficiency coefficient (EI) has been widely used. However, the EI value has been known as it is affected sensitively by big numbers among the range of numbers. In this study, a Web-based flow clustering EI estimation system using K-means clustering algorithm was developed and used for SWAT hydrology evaluation. Even though the EI of total streamflow was high, the EI values of hydrologic components (i.e., direct runoff and baseflow) were not high. Also when the EI values of flow group I and II (i.e., low and high value group) clustered from direct runoff and baseflow were computed, respectively, the EI values of them were much lower with negative EI values for some flow group comparison. The SWAT auto-calibration tool estimated values also showed negative EI values for most flow group I and II of direct runoff and baseflow although EI value of total streamflow was high. The result obtained in this study indicates that the SWAT hydrology component should be calibrated until all four positive EI values for each flow group of direct runoff and baseflow are obtained for better accuracy both in direct runoff and baseflow.